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Performance throttle body woes 

 

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 Post subject: Performance throttle body woes
Posted: Fri Sep 25, 2015 10:06 am 
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Hi guys,

I went and bought a 68mm throttle body for my 2000 AU ute (4.0, 5sp) and have had nothing but issues with it. (Yeah, I'm a numpty!)

The butterfly is closing, TPS voltages are 0.88 at closed, 4.97 at WOT.
No other mods apart from a bigger snorkel and redback cat back exhaust.

When I start it, the tacho reads 1000rpm whereas it used to run about 750rpm.
If I blip the throttle it goes to about 1800rpm, then slowly starts to come down then suddenly drops back to 1000rpm.
I cleaned the IAC valve and made a new gasket for it, but that didn't help.
The interesting thing is if I disconnect the IAC it makes virtually no difference, I thought it was supposed to stall if you did that.

I also took the battery off for a few hours.

I know there is a procedure to get the sensors right, but they're written for auto boxes, for example it tells you to put it in drive etc which obviously I cannot do :)

When driving down the road you can feel it surging slightly too.

Hoping one of you gurus can help me!

Cheers

Dave

 

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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 10:39 am 
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Check the bore of the Throttle Body and see if they have busted through the wall when they have bored it. Also check the clearance around the butterfly. If there is space around the butterfly the engine will idle high.

TPS voltages are too high.

Engine off, ignition on reds.
Closed throttle should be 0.4v - 0.8v

Wide open throttle should be no more than 4.0v

I set mine at 0.7v and wide open was 3.8v
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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 10:47 am 
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Thanks for that, I had read somewhere that the TPS voltages were higher than what you quoted so I will elongate the holes slightly on the TPS and see if I can get it down to the figures you mentioned.

The bore is fine and the butterfly is closing fully on closed throttle.

Thanks again,

Dave

 

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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 11:15 am 
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Hi Dave,

Before you start drilling the TPS holes, it sounds like there is another issue.

If it idles too high with the TPS unplugged, it is getting too much air. I suspect that the butterfly is letting through too much air. Have you tried backing out the idle adjustment screw a bit? This would also reduce your TPS idle voltage slightly.

If the idle screw is fully backed out and idle is still too high, there must be gaps around the butterfly. It may not be seating properly. If you loosen the butterfly screws slightly to allow the butterfly to seat under spring tension, then tighten them up again (in steps, alternating between them) then it should be fully seated.

Failing this, check the gasket between the TB and the manifold for leaks. Spraying Brakleen on the join will raise the RPM if there is a leak. Air entering here will raise your idle beyond what the ISC can compensate for.

 

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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 11:28 am 
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Hi

Thanks for that... I used silicon spray around the throttle body gasket and nothing happened so I grabbed some WD40 and nothing happened either.

The cam is touching the idle adjust screw and the place I bought it from said it was preset from factory so I haven't messed with it yet. I'll back it out in increments so I can put it back where it was if that doesn't help.
I'll do that before I attack the TPS with the Dremel :mrgreen:

I am positive that the butterfly is seated properly though.

Thank you

Dave

 

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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 1:01 pm 
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Thanks for that, I had read somewhere that the TPS voltages were higher than what you quoted so I will elongate the holes slightly on the TPS and see if I can get it down to the figures you mentioned.

Your high idle is caused by more than TPS voltages. You have an air leak or a vac leak somewhere.

The bore is fine and the butterfly is closing fully on closed throttle.

It may look good, but have you taken it off and checked it by holding it up to light and checking the bore

I used silicon spray around the throttle body gasket and nothing happened so I grabbed some WD40 and nothing happened either.

Silicon spray will do sweet FA, use throttle body cleaner.

The cam is touching the idle adjust screw and the place I bought it from said it was preset from factory so I haven't messed with it yet. I'll back it out in increments so I can put it back where it was if that doesn't help.

Preset from factory, my a***. They have used a second hand throttle body and modified it. They have to take evertthing off to bore it out, so who says that they put it back to "factory specs".

I'll do that before I attack the TPS with the Dremel

The TPS Voltages will still need to be adjusted but that is not what is causing the high idle.
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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 6:05 pm 
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Sounds like the butterfly isn't matching the bore.

Get a stock TB and do your own: fordmods-technical-documents-diy-f38/improving-your-6cyl-e-series-throttlebody-the-diy-way-t84040.html

 

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 Post subject: Re: Performance throttle body woes
Posted: Fri Sep 25, 2015 7:21 pm 
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Well, I took a closer look and you were right, the butterfly is very slightly open at the bottom, if you push on it gently, the revs go back to normal.

I tried unscrewing the butterfly screws as suggested, but that didn't work.
Maybe I did that part wrong.

So what I've done for now is bent the spring (I think it's for the cruise) mount so that there is more tension on the spring and that's helping out a lot.

Am going to get in touch with the seller and see what he has to say.

Thanks for all the ideas guys, appreciate it!

Dave

 

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 Post subject: Re: Performance throttle body woes
Posted: Sat Sep 26, 2015 12:01 am 
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pull the bigger tb off! and go back to stock

you dont need it :)

 

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 Post subject: Re: Performance throttle body woes
Posted: Sun Sep 27, 2015 3:28 pm 
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Well, I had a play with it yesterday and I'm not sure how I did it but she idles at 650rpm now and also dies instantly when the IAC valve was disconnected.

It also definitely seems to have made a difference when it hits about 2,500 rpm.

Much happier now, esp after seeing Disco Franks avatar!! LOL

Cheers!

Dave

 

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 Post subject: Re: Performance throttle body woes
Posted: Sun Sep 27, 2015 4:36 pm 
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You can get it to idle with the ISC valve disconnected by turning the idle adjustment screw. The screw will be backed out so far that it is trying to achieve an idle below stall point. To adjust it, the engine must be at normal operating temperature. Adjust the idle speed without ISC a little lower than the idle speed with ISC (currently 650rpm), so the idle adjustment screw is your "safety net" or backup to the ISC.

 

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